Sputtering targets are utilized in sputtering widely used in the fields of manufacturing semiconductors and flat panel displays, and the like. When sputtering the sputtering target, if the target material has therein defects, such as holes, oxides, and foreign matter, abnormal discharge may occur due to these defects. This abnormal discharge may cause a phenomenon called “splash”. The splash is a phenomenon in which a part of the target material melts, adheres to a substrate, and solidifies, and this phenomenon may cause a short circuit between wirings or electrodes with films deposited by sputtering.
To suppress abnormal discharge of the target material, target materials not containing any fine defects (e.g., 0.2 mm or more) are required. For this reason, when manufacturing the target material, it is necessary to inspect the present or absence of any defect within the target material. As the inspection method, there is a method for observing the change in reflected echo in ultrasonic waves using an ultrasonic probe.
To improve the measurement accuracy in inspection using the ultrasonic probe, the focus of the ultrasonic waves emitted from the ultrasonic probe is adjusted. A pseudo defect sample is used to adjust the focus of the ultrasonic waves emitted from the ultrasonic probe. The pseudo defect sample is provided with a hole having the same size as a fine defect in the target material. Then, the ultrasonic waves emitted from the ultrasonic flaw probe are focused on the hole, and then the reflected echo from the bottom surface of the hole is measured to adjust the sensitivity of the ultrasonic flaw detection.
JP 2010-145401 A describes pseudo defect samples. The pseudo defect sample has a counterbore and a flat-bottomed hole disposed at the bottom surface of the counterbore and having a diameter smaller than the diameter of the counterbore. The sensitivity of the ultrasonic flaw detection is adjusted by measuring the reflected echo from the bottom surface of the counterbore and the reflected echo from the bottom surface of the flat-bottomed hole.
The conventional pseudo defect sample is used to inspect defects of large-sized industrial parts. For this reason, the diameter of the flat-bottomed hole in the pseudo defect sample is set large. Hence, the ultrasonic waves emitted from the ultrasonic probe are easily focused directly on the smaller flat-bottomed hole.
However, since the conventional pseudo defect sample is not used for inspecting fine defects in the target material, in order to apply the pseudo defect sample to the target material as it is, the diameter of the flat-bottomed hole must be reduced.